1. Field of the Invention
The invention generally concerns the field of electrical discharge machining (EDM), i.e. machine tools in which an electric discharge between a wire or strip-like tool electrode and a workpiece causes material removal on the workpiece. In particular, the invention concerns a wire transport system for transporting the wire or strip-like electrode through the EDM machine and a wire cutting device to sever the wire electrode in a disposal area following the work area of the EDM machine. The invention also concerns a method for cutting of such a wire electrode.
2. Related Technology
Countless individual nonstationary electric discharges, separated from each other in space and time within a dielectric fluid occur, between a tool electrode and a workpiece in electrical discharge machining. Removal is based on extreme local heating at the location of spark discharge, during which the material evaporates. EDM machines of the type just mentioned utilize the removal effect of spark erosion. During machining the tool electrode is subject to a certain wear because of the spark discharges. For this reason the tool electrode is provided in the case of a wire erosion machine as a continuous wire electrode that passes through the work area of the EDM machine during workpiece machining and is continuously renewed.
For this purpose, a wire transport system is provided, which unwinds the wire electrode from a supply spool, guides it through the work area and transports it to a disposal area, as is known, for example, from DE 196 07 705 A1. In the disposal area the wire electrode is usually cut into small pieces a few centimeters long for space-saving disposal.
A wire cutting device is known from EP 281 511 B1 that has a rotating cutting drum and an elastic mating drum with a rubber coating rotating opposite to it. The cutting drum has cutting edges arranged parallel to the axis of rotation, which are forced against the surfaces of the mating drum during rotation of the cutting drum. The wire electrode is passed between the cutting drum and the mating drum and cut by means of the cutting edge.
This type of wire cutting device, among other things, has the shortcoming that cutting severely loads the cutting drum and the strongly abrasive wire electrode also loads the rubber coating of the mating drum. The elastic coating therefore degrades relatively quickly.
It is neither possible to deactivate the shown wire cutting device so that the wire electrode can be introduced to a disposal container uncut. This is useful, especially in wire electrodes with a diameter of 0.1 mm or less, because they require comparatively little space in the disposal container, so that cutting is not necessary for space-saving disposal. These fine wire electrodes ordinarily consist of tungsten, molybdenum or iron, i.e. materials having higher strength values relative to the conventional wire electrode materials, copper or copper-zinc alloys. The high shear strength of such wires causes additional wear during cutting.
A wire cutting device for an EDM machine is known from EP 1 153 688 A1 in which the wire electrode is guided through a guide tube to a cutting area in which one end of the guide tube forms a cutting edge. A rotating cutting drum with cutting edges arranged essentially parallel to the axis of rotation is arranged on the end of the guide tube so that the cutting edge of the cutting drum is moved transversely over the end of the guide tube and grasps and severs the wire electrode pushed forward on this account.
In this wire cutting device it is neither possible to deactivate the wire cutting device with small diameters of the wire electrode easily so that the wire electrodes can be guided into the disposal area uncut.